21618531 has 24 divisors (see below), whose sum is σ = 34332480. Its totient is φ = 12999600.

The previous prime is 21618517. The next prime is 21618533. The reversal of 21618531 is 13581612.

It is not a de Polignac number, because 21618531 - 2⁷ = 21618403 is a prime.

It is a super-2 number, since 2×21618531² = 934721765195922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21618495 and 21618504.

It is not an unprimeable number, because it can be changed into a prime (21618533) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 12976 + ... + 14546.

It is an arithmetic number, because the mean of its divisors is an integer number (1430520).

Almost surely, 2^21618531 is an apocalyptic number.

21618531 is a deficient number, since it is larger than the sum of its proper divisors (12713949).

21618531 is a wasteful number, since it uses less digits than its factorization.

21618531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1727 (or 1724 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21618531 is about 4649.5732062201. The cubic root of 21618531 is about 278.5749491806.

The spelling of 21618531 in words is "twenty-one million, six hundred eighteen thousand, five hundred thirty-one".